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New Antennae

 
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speedy11



Joined: 29 Jun 2015
Posts: 42
Location: Port Orange, FL

PostPosted: Tue May 08, 2018 7:06 am    Post subject: New Antennae Reply with quote

I am installing two new antennae - one Comant 122 for comm and one standard ball tipped 3 inch transponder=type for an Echo UAT.
I am retaining two older antennae - one comm and one transponder. The real estate for mounting is limited since they are all mounted on the fuselage underside of an RV-8. I should be able to come close to the desired one meter separation between all antennae.
My question is - do I need to remove exterior paint and interior primer paint at the mounting location of the new antennae? Or is the mounting screw contact sufficient to connect with the ground plane? I will, of course, have a doubler for mounting each antenna.
Thanks
Stan Sutterfield


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PostPosted: Tue May 08, 2018 8:43 am    Post subject: New Antennae Reply with quote

At 10:04 AM 5/8/2018, you wrote:
Quote:
I am installing two new antennae - one Comant 122 for comm and one standard ball tipped 3 inch transponder=type for an Echo UAT.
I am retaining two older antennae - one comm and one transponder. The real estate for mounting is limited since they are all mounted on the fuselage underside of an RV-8. I should be able to come close to the desired one meter separation between all antennae.
My question is - do I need to remove exterior paint and interior primer paint at the mounting location of the new antennae? Or is the mounting screw contact sufficient to connect with the ground plane? I will, of course, have a doubler for mounting each antenna.
Thanks
Stan Sutterfield



https://goo.gl/skAS8R



Bob . . .


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speedy11



Joined: 29 Jun 2015
Posts: 42
Location: Port Orange, FL

PostPosted: Tue May 08, 2018 1:44 pm    Post subject: Re: New Antennae Reply with quote

Perfect. Thanks, Bob.
Stan


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BARRY CHECK 6



Joined: 15 Mar 2011
Posts: 687

PostPosted: Wed May 09, 2018 8:15 am    Post subject: New Antennae Reply with quote

I'm not  sure who asked the question...
You DO NOT remove paint from  the exterior of the plane.
You do need a GOOD electrical connection between the antenna and the plane to create a Ground Plane.
I have found many antennas be painted or powder coated which reduces/elininates the electrical contact area.  
My trick is to make sure the Mounting Hole Area of the antenna makes a good electrical ground connection with the Screws.
To do this I remove the paint INSIDE of the screw counter-sink.  I do this with a 100 deg counter-sink tool.
The next part of the trick to to make the through hole on the Plane a nice small tight fit so the screw has to be SCREWED into/through the skin.
As for the interior primer...  It is a Paint primer or Chem-Film Primer?
Paint - YES, it has to be removed ONLY in the area around screws.  NOT the entire area.
Chem-Film - NO, it does not have to be remove UNLESS it is VERY dark in color.  Darker Chem-Film can be insulation.
Not sure which level you have?  REMOVE IT!  Using Scotch Brite.  Again, you only need the area around the screw for the diameter of the washer/lock washer.
You can do a simple check to the quality of your work by taking a resistance reading from the antenna to a remote part of the plane.  ZERO OHMS is what you are looking  for.
After you are all done with the mounting and testing you can paint over the external screw heads sealing off moisture.
As for the area around the external antenna mount...  Do what the manufacture recommends - gasket and/or RTV.
I like using RTV as a sealant even with a gasket.
Barry


On Tue, May 8, 2018 at 12:42 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
Quote:
At 10:04 AM 5/8/2018, you wrote:
Quote:
I am installing two new antennae - one Comant 122 for comm and one standard ball tipped 3 inch transponder=type for an Echo UAT.
I am retaining two older antennae - one comm and one transponder.  The real estate for mounting is limited since they are all mounted on the fuselage underside of an RV-8.  I should be able to come close to the desired one meter separation between all antennae.
My question is - do I need to remove exterior paint and interior primer paint at the mounting location of the new antennae?  Or is the mounting screw contact sufficient to connect with the ground plane?  I will, of course, have a doubler for mounting each antenna.
Thanks
Stan Sutterfield



https://goo.gl/skAS8R



  Bob . . .


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cluros(at)gmail.com
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PostPosted: Wed May 09, 2018 8:56 am    Post subject: New Antennae Reply with quote

Barry, default text size setting should be normal, yours is set to large. Normal is fine for most of us and for anyone that needs larger can do so at their end.

As for antenna grounding, I would stick with the manufacturer's instructions. For example:
From COMANT

Aircraft Skin Surface and Mounting Preparation
The electrical bonding of the antenna to the aircraft ground is highly important. If this is not done properly, antenna performance characteristics may become distorted and nulls may appear in the antenna radiation pattern. This, in turn, may cause erratic navigational readings or signal drop out. The electrical bonding of the antennas to the aircraft skin is best accomplished by direct metal-to metal contact of the antenna base to the aircraft skin. To accomplish this, the aircraft paint in the mounting area will need to be removed and the surface alodined to protect aluminum against corrosion. An alternate method for providing electrical bonding is through the mounting screws, which attach to a backing plate inside the aircraft skin. Remove any interior paint in the area where the backing plate is placed to assure a good ground. Coat this area with alodine to minimize corrosion. To test the electrical bonding of the blade to the aircraft, a reading of .003 ohms between the antenna base plate and ground should be achieved.

From RAMI
CLEAN METAL SURFACE FOR GOOD GROUND CONNECTION
[img]cid:ii_jgzca7dg0_16345cefb2ed3089[/img]



On Wed, May 9, 2018 at 8:00 AM, FLYaDIVE <flyadive(at)gmail.com (flyadive(at)gmail.com)> wrote:
Quote:
I'm not  sure who asked the question...
You DO NOT remove paint from  the exterior of the plane.
You do need a GOOD electrical connection between the antenna and the plane to create a Ground Plane.
I have found many antennas be painted or powder coated which reduces/elininates the electrical contact area.  
My trick is to make sure the Mounting Hole Area of the antenna makes a good electrical ground connection with the Screws.
To do this I remove the paint INSIDE of the screw counter-sink.  I do this with a 100 deg counter-sink tool.
The next part of the trick to to make the through hole on the Plane a nice small tight fit so the screw has to be SCREWED into/through the skin.
As for the interior primer...  It is a Paint primer or Chem-Film Primer?
Paint - YES, it has to be removed ONLY in the area around screws.  NOT the entire area.
Chem-Film - NO, it does not have to be remove UNLESS it is VERY dark in color.  Darker Chem-Film can be insulation.
Not sure which level you have?  REMOVE IT!  Using Scotch Brite.  Again, you only need the area around the screw for the diameter of the washer/lock washer.
You can do a simple check to the quality of your work by taking a resistance reading from the antenna to a remote part of the plane.  ZERO OHMS is what you are looking  for.
After you are all done with the mounting and testing you can paint over the external screw heads sealing off moisture.
As for the area around the external antenna mount...  Do what the manufacture recommends - gasket and/or RTV.
I like using RTV as a sealant even with a gasket.
Barry


On Tue, May 8, 2018 at 12:42 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
Quote:
At 10:04 AM 5/8/2018, you wrote:
Quote:
I am installing two new antennae - one Comant 122 for comm and one standard ball tipped 3 inch transponder=type for an Echo UAT.
I am retaining two older antennae - one comm and one transponder.  The real estate for mounting is limited since they are all mounted on the fuselage underside of an RV-8.  I should be able to come close to the desired one meter separation between all antennae.
My question is - do I need to remove exterior paint and interior primer paint at the mounting location of the new antennae?  Or is the mounting screw contact sufficient to connect with the ground plane?  I will, of course, have a doubler for mounting each antenna.
Thanks
Stan Sutterfield



https://goo.gl/skAS8R



  Bob . . .



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speedy11



Joined: 29 Jun 2015
Posts: 42
Location: Port Orange, FL

PostPosted: Wed May 09, 2018 10:45 am    Post subject: Re: New Antennae Reply with quote

Excellent info.
Thanks to everyone.
Stan Sutterfield


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BARRY CHECK 6



Joined: 15 Mar 2011
Posts: 687

PostPosted: Wed May 09, 2018 11:15 am    Post subject: New Antennae Reply with quote

Sebastien:

So, how does my instructions differ from the manufactures?

Quote:
From your re-post of there instructions their very first line states: "The
electrical bonding of the antenna to the aircraft ground is highly

important." Electrical Bonding!
Of course the good physical bonding is done by the four (4) mounting screws


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Kellym



Joined: 10 Jan 2006
Posts: 1539
Location: Sun Lakes AZ

PostPosted: Wed May 09, 2018 12:39 pm    Post subject: New Antennae Reply with quote

Barry has the technique correct. I don't know why Comant even recites
the paint removal method. Removing aircraft exterior paint for grounding
is just asking for corrosion. Read their alternate method included in
your quote.
Normally one fabricates a doubler plate to go on the inside of the skin.
Nutplates are riveted to the doubler. You can scuff the inside skin for
grounding, or you can just use 4-6 rivets to flush rivet the doubler to
the aircraft skin. Either way, the ground path is through the screws and
the doubler should make good ground contact to the screws and the airframe.
That is the technique I used for both of the CI-122s I have on my RV,
and get excellent reception and no complaints on transmit.
Kelly
A&P/IA

On 5/9/2018 9:54 AM, Sebastien wrote:
Quote:
Barry, default text size setting should be normal, yours is set to
large. Normal is fine for most of us and for anyone that needs larger
can do so at their end.

As for antenna grounding, I would stick with the manufacturer's
instructions. For example:

From COMANT

An alternate
method for providing electrical bonding is through the mounting screws,
which attach to a backing plate inside the aircraft skin. Remove any
interior paint in the area where the backing plate is placed to assure a
good ground. Coat this area with alodine to minimize corrosion. To test
the electrical bonding of the blade to the aircraft, a reading of .003
ohms between the antenna base plate and ground should be achieved.

From RAMI

CLEAN METAL SURFACE FOR GOOD GROUND CONNECTION



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_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD
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PostPosted: Wed May 09, 2018 1:29 pm    Post subject: New Antennae Reply with quote

Quote:
Also, the Manufacture's last capitalized line reads: CLEAN METAL SURFACE FOR GOOD GROUND CONNECTION
and is repeated again with RED underlining.
It does NOT say the entire area under the antenna.

Which is what the 'bonding circles' around
the screw holes are about along with maximizing
compression of the various layers at each
joint. These make up gas-tight interfaces that
will repel oxygen/moisture. Again, another good
place for a bit of DC-4 around the hole before
bolting the antenna down.

Our readers don't have bonding meters and have
generally done well without them. I used to
offer one and we did sell about a dozen . . .

https://goo.gl/1X6S6b

They're based on this article I did originally for
Raytheon-Beech field techs.

https://goo.gl/grXUex

To be sure, tens of thousands of antennas have
been installed with the gaskets . . . but if
you're interested in MAINTAINING mate up
forces in the mounting bolts, sticking any
'squishy' stuff in the gap tends to degrade
those forces with age.



Bob . . .


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